[gtkmm/gtkmm-3-24] MSVC_NMake/README: Update build info

[Chun-wei Fan <fanchunwei src gnome org>]

commit b0f3693183fade7cbc332435d6e02a2f27e4d504
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Tue Jun 30 15:11:06 2020 +0800

    MSVC_NMake/README: Update build info
    
    Note that it is possible to build with Visual Studio with Meson, on the
    condition that the -mm dependencies are built with Meson as well, since we need
    their pkg-config files.
    
    Also note that the same compiler version should be used to build gtkmm and the
    -mm dependencies, even for Visual Studio 2015, 2017 and 2019.

 MSVC_NMake/README | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/MSVC_NMake/README b/MSVC_NMake/README
index 678546d3..1f9084c7 100644
--- a/MSVC_NMake/README
+++ b/MSVC_NMake/README
@@ -1,9 +1,13 @@
 Building gtkmm-3.0 with Visual Studio 2013 or later
 
 * You will need Visual Studio 2013 (MSVC 12.0) or later. Earlier versions of the compiler, including 11.0
-  and earlier will not work.
+  and earlier will not work.  The build can be carried out using the NMake Makefiles supplied in this
+  directory, or via using Meson.  Meson is only supported if libsigc++, glibmm, cairomm, atkmm and pangomm
+  are built with Meson as well.
 * Install the latest Win32 GTK+ Development files from ftp://ftp.gnome.org/pub/GNOME/binaries/win32/gtk+
-* Build libsigc++, glibmm, cairomm atkmm and pangomm from source.
+* Build libsigc++, glibmm, cairomm atkmm and pangomm from source, with the same compiler version, even if
+  on Visual Studio 2015, 2017 or 2019.  If there are strange linker errors, they are likely caused by
+  mixing different compiler versions.
 * Use the Visual Studio command prompt that is appropriate for your build and navigate to this directory.
 * Run nmake /f Makefile.vc CFG=[debug|release].  Also pass in PREFIX=<path> to this command line if
   GTK+, libsigc++, glibmm, cairomm, atkmm and pangomm are not in $(srcroot)\..\vs[12|14|15]\$(platform).